How to Wire a Tachometer | It Still Runs A secure ground connection will help the tachometer to run correctly. Connect the green wire to the negative post of an existing electronic coil or Electronic ignition system using a tachometer Electronic Tachometer – Circuit Wiring Diagrams Tachometer schematic note : I did not test tachometer schematic on any car. Installing it on the car, all the responsibility you take on. However, the signals from my function generator tachometer worked fine. The voltage on the high-voltage wire connector coming from the ignition coil reaches several kilovolts.